Optimization of the catalytic asymmetric addition of nitroalkanes to cyclic enones with trans-4,5-methano-L-proline

The conjugate addition of symmetrical 2-nitroalkanes to 2-cycloalkenones catalyzed by trans-4,5-methano-L-proline proceeds with > 99% ee and excellent chemical yields. 1-Nitroalkanes afford diastereomeric syn/anti products that can be separated with good individual enantioselectivities. Proline hydroxamic acid and its trans-4,5-methano-L-proline hydroxamic acid are also effective organocatalysts in the addition of 2-nitropropane to 2-cyclohexenone (75% and 81% ee, respectively).